Neuromuscular transmission may be defined as the transfer of a motor impulse between a nerve and a muscle in the neuromuscular junction. This transmission may be blocked through the use of muscle relaxants. Muscle relaxation may be used during surgery under general anaesthesia to allow e.g. endotracheal intubation and, in general, to provide the surgeon with the optimum working conditions depending on the type of intervention.
When muscle relaxants during surgery are used, it is very important to monitor the patient's neuromuscular blockade status. For such a monitoring, a peripheral motor nerve may be electrically stimulated and muscle response(s) to said stimulation may be processed to infer the neuromuscular blockade status. In clinical practice, various stimulation patterns may be used for different purposes and in different phases of the operation.
Systems and methods are known based on the above principles. These systems may comprise electrodes for electro stimulating the patient and sensors for detecting a response to the electro-stimulation.
The electrodes may be connected to a provider of electro-stimulation signals for receiving suitable signals from the provider. The electrodes may be attached to the skin of the patient at a body part suitable for stimulating a particular motor nerve, such as e.g. ulnar nerve.
The sensors may comprise e.g. an accelerometer attached to e.g. a fingertip of the patient for sensing the movement of the finger as a reaction to the electro-stimulation. The sensors may be connected to a sensing unit in such a way that signals from the sensor(s) are received by the sensing unit and processed to generate data representing a response to the electro-stimulation.
The electrodes and sensors may therefore be arranged separately on different parts of the body. This dispersion of the electrodes and sensors may make the set-up of the system time-consuming and the subsequent use of the system cumbersome, which may generate discomfort to the surgical team during surgery. It can even lead to surgeons and/or anaesthesiologists disregarding these systems during surgery.
The provider of electro-stimulation signals and the sensing unit may be integrated in a single monitor. The electrodes may be connected to the monitor through cables, and the sensors may be connected to the monitor through further cables. Therefore, various cables may be present between the patient and the monitor when the electrodes and sensors are attached to the patient.
Having such a plurality of cables between the monitor and the patient may be annoying for the surgical staff and may be a source of problems during surgery. For example, somebody may accidentally stumble into/over a cable and/or a tangle of cables may occur. This may cause detachment of an electrode/sensor from the patient and/or disconnection of the cable from the monitor.
U.S. Pat. No. 5,957,860A discloses an apparatus comprising means for stimulating a nerve (e.g. electrodes) and means for detecting a response to the stimulation. The apparatus is characterized in that said means are provided in a single body, which is a pressure cuff of the type generally used for measuring arterial pressure, provided with or connected to means for pressure detection. With this apparatus, the previously discussed problem about dispersion of electrodes and sensors is avoided, since they are provided in a single body.
U.S. Pat. No. 5,957,860A further discloses that the pressure cuff and integrated electrodes may be connected to a monitor through a tube configured to conduct both air and electricity. The monitor may send suitable electro-stimulation signals to the electrodes for muscle stimulation through said single tube. The monitor may also receive pressure variations in the cuff (representing a response to the muscle stimulation) also through said single tube. Hence, the previously discussed problem related to the presence of a plurality of cables between the patient and the monitor is avoided with this configuration.
The monitor may be adapted to receive instructions or parameters provided by an anaesthesiologist (or similar profile) for the monitor to transmit suitable stimulation signals to the electrodes according to said instructions or parameters. For instance, data on stimulation pattern(s) to be used at each time, periodicity of the signals, intensity of the signals, etc. may be provided by the anaesthesiologist to the monitor through suitable data entry means (e.g. a keyboard).
The monitor may also be adapted to receive signals from the sensors (accelerometer, cuff, etc.) and to process them in such a way that a representation of them may be provided to a display. This representation of the sensor signals may be displayed in the form of numerical values (e.g. percentages), graphics, etc. in such a way that the anaesthesiologist may derive a muscle response to the performed electro-stimulation.
It is known that the anaesthesiologist can test (or monitor) a neuromuscular blockade status for a patient by paying attention to the display and manually acting on the monitor depending on the muscle responses derived from the displayed data. Manually acting on the monitor may comprise providing new instructions/parameters to the monitor in order to cause the transmission of new stimulations signals with e.g. different intensity, or frequency or stimulation patterns depending on the new circumstances.
Several iterations of deriving muscle responses (from displayed data) and optionally acting on the monitor may be performed by the anaesthesiologist for finally achieving a target neuromuscular blockade status for the patient. This may be labour-intensive, time-consuming and cumbersome for the anaesthesiologist and may generate inefficiencies and/or deficiencies in the process of relaxation (i.e. the initial induction, subsequent maintenance, and eventual reversal of a drug-induced neuromuscular blockade status) of the patient.
Since the above method of monitoring (or testing) a neuromuscular blockade status highly depends on the attention paid by the anaesthesiologist, a delay between achievement of a neuromuscular status and corresponding actions on the monitor may occur. Delayed actuations may generate inefficiencies in terms of e.g. extending the occupation of an operating room, using greater amounts of muscle relaxant than really needed, etc.
Furthermore, in an Operating Room, momentary situations of high stress may exist so that an anaesthesiologist may miss the result of a precise electro-stimulation or may lose track of how many stimulations have been performed and previous results.
Said dependence on the anaesthesiologist's attention may also cause the anaesthesiologist to act erroneously on the monitor as a consequence of e.g. a wrong derivation of a muscle response from the displayed data. Wrong actuations by the anaesthesiologist may e.g. generate damage or risk of damage to the patient, which have to be attenuated during surgery. In this case, more surgical resources may be finally used than initially required.
In apparatuses based on obtaining or deriving muscle responses depending on how pressure varies in a pressure cuff (such as e.g. the one disclosed in U.S. Pat. No. 5,957,860A), patient's heartbeats may create interferences that may distort the muscle response. Hence, subsequent actions and/or assessments based on said distorted responses may generate errors in e.g. monitoring (or testing) a neuromuscular blockade status for a patient.
Electro-stimulation electrodes are known for their application on the skin of a patient. These electrodes, which may be suitable for applications as the ones described before, may comprise a support layer and an electrically conductive material (or medium). The support layer may be made of an electrically insulating material and may be configured in such a way that, in use, a surface of the support layer contacts the skin of the patient.
The support layer may comprise at least one region having one or more holes. The electrically conductive medium may be adhered to a surface of the support layer which may be the opposite to the surface of contact with the skin of the patient. The electrically conductive medium generally extends over the holes and a conductive layer is interposed in between for conveying current to the skin.
A risk of this structure may be that the conductive layer may be torn or damaged at the level of the region of contact with the patient's skin and, therefore, the electrically conductive medium may come into direct contact with the skin. In these circumstances, a concentrated and relatively high current may be transmitted to the patient's skin.
Such a concentration of electrical energy may cause e.g. a burn on the skin of the patient, who may be under general anaesthesia if the patient is being subjected to a surgical operation. In this situation, the patient may thus not be able to alert the medical team about the damage he/she is suffering.
Connectors for electro-stimulation cuffs, or compressive armbands, are known configured to connect a tube for the conveyance of pressurized air to the cuff. These connectors may comprise a body comprising a base and a tubular portion arranged on one face of the base for the coupling of the tube.
These connectors may further comprise two connection electrodes having external terminals for connection with external cables, and internal terminals for connection to conductive tracks internal to the cuff. Such a special type of connectors which feature the ability of simultaneously conveying both pressurized air and electrical signals are referred herein as Hybrid Connectors.
Hybrid Connectors for electro-stimulation cuffs should ideally fulfil at least some of the following requirements:
a) transmission of electrical stimuli emitted from a monitor and conveyed through conductive wires electrically connecting the monitor to the pressure cuff, for finally discharging the electrical stimuli onto the patient's skin through corresponding electrodes.
b) entry of pressurized air into the bag of the compressive armband during the inflation phase thereof, and subsequent free evacuation of the air to e.g. the monitor and, from there, to the atmosphere.
c) pneumatic air tightness of the connection between the inflatable bag and the hybrid connector, without requiring the application of glues, adhesives, or any other type of sealant of chemical nature. A risk associated with such sealants may be that they can deteriorate over time and, therefore, air leakages may occur. Moreover, UNE-EN ISO 10.993 standards about “Bio-Compatibility of Medical Devices” may not be suitably fulfilled with the use of such sealants.
d) protection against intrusions (of liquids and/or dust) in the junction between the tube and the hybrid connector. Such intrusions can short-circuit the conveyance of electrical stimuli which may put at risk the physical integrity of the patient and/or surgery staff.
e) mechanical resistance of the junction between the tube and the hybrid connector without requiring the application of glues, adhesives, or any other type of sealant of chemical nature. This requirement is aimed at preventing that an excessive pulling of the tube (e.g. accidentally performed by its unnoticed dragging because of the busy circulation of the operation room's staff around the surgical table) could pull out the tube from its receptacle in the hybrid connector.
f) skin friendly nature since the hybrid connector may rest during surgery on a delicate skin covering the internal crook of the patient's arm. With this requirement, e.g. skin lacerations or irritations thereto may therefore be prevented.
U.S. Pat. No. 5,957,860A discloses a pressure cuff with two integrated electrodes for electro-stimulating a peripheral motor nerve of a patient. The electro-stimulation of the nerve may cause an evoked muscle response which may be evaluated in terms of a steep change in the air pressure inside an inflatable bag of the cuff. The magnitude of this air pressure change may determine, by using an appropriate computing algorithm, an indicator about the neuromuscular blockade status of the patient.
The electrodes include an active electrode (cathode or negative lead, through which current is supplied) and a passive electrode (anode or positive lead, through which current is collected). In between the electrodes, the current passes through a patient's limb, in particular a patient's arm.
FIG. 27a schematically shows a prior art pressure cuff 270 which comprises a first electro-stimulation electrode 273 and a second electro-stimulation electrode 274. The pressure cuff is shown further comprising an inflatable bag 275, and a flexible tube 276 for conducting air and electrical current between the cuff and a monitor or similar device configured to operate the cuff. As shown in FIG. 27c, the pressure cuff 70 has a length L and a width W.
FIG. 27a also illustrates a theoretical line 271 representing a path of a nerve to be electro-stimulated through the electrodes 273, 274. The pressure cuff 270 is configured in such a way that, in use, the electrodes 273, 274 are arranged on a region of the limb which is at least partially on or “over” the nerve (theoretically represented by the line 271).
FIG. 27b offers an enlarged view of a region 272 indicated in FIG. 27a and from a point of view 277 also indicated in FIG. 27a. 
As shown in FIG. 27c, the pressure cuff 270 is configured to be preferentially arranged around a patient's right limb (either arm or leg) with the first and second electrodes 273, 274 and the inflatable bag 275 being suitable arranged according to the following requirements:
The first electrode 273 functions as the anode (or positive lead) and is arranged in a proximal position on an ulnar nerve 278, and the second electrode 274 functions as the cathode (or negative lead) and is arranged in a distal position on the ulnar nerve 278. The particular requirements further comprise the inflatable bag 275 arranged on or over a brachial artery 279.
Pflüger's Law defines the conditions under which an active electrode 274 and a passive electrode 273 arranged on a path of a motor nerve 278 ensure that an evoked muscle response induced by a current transmitted by the active electrode 274 to the nerve 278 is reliable.
As shown in Table 1, this Law concludes that only when the active electrode 274 is in a distal position and the passive electrode 273 is in a proximal position, the evoked muscle response will reliably occur irrespective of the magnitude of the intensity of the current transmitted by the active electrode 274.
Herein, distal position refers to a distal position in the corresponding patient's limb with respect to the patient's trunk, and proximal position refers to a proximal position in the corresponding patient's limb with respect to the patient's trunk.
According to Pflüger's Law, an electro-stimulation performed by two electrodes 273, 274 placed on a motor nerve 278 can cause an evoked muscular response (described as “twitch” in Table 1) depending on two parameters. A first parameter refers to the intensity of the current generated to electro-stimulate the motor nerve 278, and a second parameter refers to the relative position of the electrodes 273, 274 on the path of the nerve 278. This second parameter is technically called “polarity”.
Table 1 provides detailed data about this phenomenon. The term ON refers to the moment at which the electrical stimulus is actually applied to the nerve (closed circuit condition) and the term OFF refers to the moment at which the electrical stimulus is withdrawn (open circuit condition).
TABLE 1POLARITYACTIVE ONACTIVE ONELECTRICPROXIMALDISTALCURRENTONOFFONOFFWEAKTwitchNo twitchTwitchNo twitchMEDIUMTwitchTwitchTwitchTwitchSTRONGNoTwitchTwitchNo twitchtwitch
In Table 1, three different intensities for the electrical current applied for electro-stimulation are considered: WEAK, MEDIUM and STRONG. The content of Table 1 permits deriving that a reliable muscle response can be obtained, irrespective of whether the intensity of the stimulating current is WEAK, MEDIUM or STRONG, only when the active electrode 274 is arranged in a distal position with respect to the passive electrode 273, as shown in FIG. 27c. 
However, when the same pressure cuff is changed to a patient's left arm, the practitioner is now forced to rotate the pressure cuff 180° in order to—as shown in FIG. 27d-match the position of both the stimulating electrodes 273, 274 and the inflatable bag 275 with—respectively—the course of the peripheral motor nerve 278 and the brachial artery 279 on the patient's left arm. By doing so, nevertheless, the passive and active electrodes 273, 274 of the pressure cuff 270 will then unavoidably be laid out on the motor nerve 278 according to the “ACTIVE ON PROXIMAL” arrangement (as identified in Table 1).
As shown in Table 1, such an “ACTIVE ON PROXIMAL” arrangement suffers from the important limitation of not being able to warrant an effective evoked muscle response (TWITCH) after applying (ON) a stimulating current of STRONG intensity on the motor nerve.
This electro-physiological phenomenon is technically known as “Anodal Block of Conduction”, which refers to the lack of evoked muscular response featured on a patient's muscle, when the motor nerve innervating said muscle is stimulated with a high electrical current intensity using a particular layout of electrodes.
This particular layout comprises the passive electrode (anode, positive lead) of the stimulating circuit placed further distal on the path of the motor nerve than the active electrode (cathode, negative lead). Such a scenario is referred to as “No Twitch” in Table 1, “ACTIVE ON PROXIMAL” Polarity, “ON” column, and “STRONG” Electric Current's row.
Said “Anodal Block of Conduction” has its root in the appearance of a positively charged electrical field under the passive electrode of the stimulating circuit, when said circuit is closed (ON in terms of Table 1). The existence of such a positively charged electric field leads to the so-called hyperpolarization of the nerve's trunk outer membrane. The magnitude of such a hyperpolarization is directly proportional to the strength of the positively charged electrical field, which is, in turn, directly proportional to the intensity of the electrical current applied for stimulating the nerve.
The propagation of a nervous impulse along a nerve's trunk could be assumed as being a propagation of a negatively charged electrical wave along the nerve. Therefore, a positively charged electrical field anywhere on the nerve's trunk between the active electrode and the innervated muscle may act as an electrical barrier for the propagation of the cited negatively charged electrical wave. Hence, the positively charged electrical field may block, below the passive electrode or anode (this explains the term “Anodal Block”), the eventual arrival of the electrical nerve impulse to the muscle of interest.
The unnoticed appearance of the “Anodal Block of Conduction” phenomenon may constitute a potential source of medical errors during the assessment of the neuromuscular blockade condition of a patient, primarily when stimulating a patient's peripheral motor nerve according to an “ACTIVE ON PROXIMAL” electrodes' set-up with a STRONG electrical current stimulation intensity. If no muscle response is obtained, the anesthetist may incorrectly diagnose that the patient is in a deep blockade condition whereas the patient might actually be in a non-blocked condition.
Such an observed lack of motor response may actually be caused by the undesired blockade of the nervous signal's propagation at the strongly hyperpolarized nerve's section under the passive electrode, which may be placed further distal on the path of the motor nerve which has been stimulated upstream.
At the current day, the only way to prevent the occurrence of the “Anodal Block of Conduction” phenomenon is to actively invert, through corresponding software, the Polarity of the electrodes when the pressure cuff is arranged around a left limb. However, as such a reversal operation has to be manually carried out by the practitioner on e.g. a console, monitor or similar, this solution is not failure proof.
Pressure cuffs incorporating electro-stimulation circuits are known from U.S. Pat. No. 5,957,860A. Such electro-stimulation circuits may comprise electrodes and related connections which are made with conventional electric components such as e.g. metallic plates for the electrodes and metallic wires for the connection of the electrodes to a corresponding electricity source.
This kind of electro-stimulation circuits incorporated in a pressure cuff may be relatively stiff, voluminous, and non-ergonomic, so that they may be annoying to the patient to whom the circuit is applied for electro-stimulation. Moreover, the fabrication of said circuits may be complicated and time-consuming because a relative large number of manual actions may be required.
The attachment of these electro-stimulation circuits to the pressure cuff may comprise adhesives or similar substances which may cause alterations, such as e.g. irritation, of the skin of the patient to which the circuit is applied for electro-stimulation.
The present disclosure aims at improving upon the prior art methods of monitoring a neuromuscular blockade status and systems suitable for such methods.